4 J. H. Smith, Bleach-out Process of Colour Photography. 



The light passing through the red of the original bleaches 

 the blue-green but not the yellow or the pink, and 

 these colours combined reproduce the orange-red of 

 the original in the copy ; yellow or red plus green light 

 bleaches both blue-green and pink leaving yellow, green 

 light bleaches pink leaving blue-green and yellow pro- 

 ducing green again in the copy ; blue-green, allowing 

 green and blue light to pass, bleaches the yellow and pink 

 dyes leaving the blue-green in the copy ; blue-violet 

 bleaches the yellow dye leaving the blue-green and pink 

 dyes producing the original blue-violet in the copy while 

 the pink allowing blue-violet and orange-red to pass 

 bleaches out the yellow and blue-green dyes leaving the 

 pink dye intact. As the black band allows no light to 

 pass, all three dyes in the film remain unbleached leaving 

 the black film unaffected. Other coloured mixtures, and 

 varied coloured intensities, or mixtures with grey, etc , in 

 the original are reproduced in the copy by partial or more 

 intense bleaching, etc., of the corresponding comple- 

 mentary dyes in the film. 



Vallot (6) in 1895, and Neuhauss (7) and Worel (8) in 

 1902 were the first practical workers in this interesting 

 field, and some of the results obtained were fairly satis- 

 factory for the conditions obtaining at that time. Neuhauss 

 had difficulties in getting results on paper, so he coated 

 his emulsions on glass and opal. Worel did not emulsify 

 his dyes, but used simply dye solutions which he trans- 

 ferred to paper. He discovered the use of anethol as a 

 sensitiser for the dyes. Neuhauss used peroxide of 

 hydrogen as a sensitiser, and was even able to obtain 

 direct photographs in colours in the camera with very 

 long exposures. The dyes he employed were erythrosine, 

 auramine and methylene-blue. Worel employed victoria- 

 blue and curcumine. 



